Planted Tank Guru
Join Date: Feb 2010
Location: Newbury Park, CA
I'd double up on the dosing and lengthen the day rather than cut back. Elodea is a fast growing weed and nutrient hogs. GSA is an indicator of low phosphate and probably low CO2. Your light isn't particularly bright for the tank, I would keep it at 8 hours or increase a bit to see if that help. I would dose more for a couple weeks to see if things improve then change the light period rather than do it all at once.
Check the actual pH of the water before CO2 goes on, just as the lights go on and when the drop checker is finally showing yellow. The last two should be nearly the same, the first should be at its highest point and the same as if you dipped out a cup of tank water and left it for 24 hours. If the second pH is much lower than the third either increase the flow around your diffuser or turn the CO2 on earlier. Your setup seems fine to me and your CO2 is getting around the tank fine though. Do you have a nice ripple on the surface? You can increase the CO2 delivered if O2 is in good supply.
I put a sprig of hornwort, an infamous weed, in the tank a few months ago. My tank has been up since October and has lots of nutrients, CO2 and light and plants grow pretty fast and mostly algae free. It looked horrible for a couple weeks. New growth happened but it turned brown pretty fast. After about a month it finally adjusted and today I am going to weigh what is in the tank after 4 days growth. Started with 50 grams, looks like at least 100 and possibly more today. Keep at it, the plants could still be in adjustment phase.
As for the cleaning crew otos are great. I figure there are lots of different kinds of grazing critters and have 4 different mouth styles in the tank. Snails, platies, otos and bristlenose plecos. Shrimp and snails would be good but with the fish load it is unlikely they would be able to do much before they become a tasty meal. Angels nibble at algae, don't know if loaches or gouramis do or not.
Try to grow healthy plants rather than eliminate algae though. Fertilizer is and light may need to be increased to get that and grazers are a help but don't count on them to polish the tank clean.